Mobile terminals such as mobile POS (Points of Sales) and PDA (Personal Digital Assistants) should be turned off whenever not in use to limit battery consumption as much as possible but are preferably quickly ready for use when necessary. As a result, some mobile terminals have a suspend/resume function (hereinbelow referred to as simply a “suspend function”).
According to the suspend function, when the power-supply switch is turned OFF, the state of the terminal immediately preceding turning OFF the power-supply switch is saved, and when the power-supply switch is subsequently turned ON, the state of the terminal immediately preceding turning OFF the power-supply switch is restored. According to this function, the operator of the mobile terminal, when turning ON the power-supply switch, is able to resume work from the state that immediately preceded turning OFF the power-supply switch. This effect is obtained because the supply of power is continued to parts of the device even while the power-supply switch is in the OFF state, but while the suspend function is operating, power consumption is low compared to the state in which the power-supply switch is in the ON state and consumption of the battery is therefore limited. The standby state in which the state of the terminal immediately preceding turning OFF the power-supply switch is saved is hereinbelow referred to as the suspend state. The suspend state is also assumed to include a function by which, without the power-supply switch being turned OFF, a terminal transitions to the power-saving suspend state with the power-supply switch in the ON state after the passage of a fixed interval with no input such as key-in. In this case, the state of the terminal immediately preceding transitioning to the power-saving suspend state is saved, and when the power-saving suspend state is subsequently canceled by, for example, key-input, the state of the terminal that immediately preceded the transition to the power-saving suspend state is revived.
On the other hand, a mobile POS that is capable of data processing for credit card payments handles personal information that is to be concealed such as credit card numbers and therefore requires measures for preventing the falsification of information that is recorded in memory. A tamper-detection circuit, which is a circuit for protecting information that is recorded in memory, is therefore provided in a mobile POS of this type. Power is supplied to the tamper-detection circuit and operation of the tamper-detection circuit is maintained even when the power-supply switch of the main unit of the mobile POS is in the OFF state.
The configuration of a mobile terminal of the related art that is provided with the above-described suspend function and tamper-detection circuit is next described.
FIG. 1 and FIG. 2 are block diagrams showing an example of the configuration of a mobile terminal of the related art. FIG. 1 is a figure for explaining the normal state of use in which the power-supply switch is ON, and FIG. 2 is for explaining the suspend state.
As shown in FIG. 1, mobile terminal 100 includes: LCD (Liquid Crystal Display) 11 that is the display unit; information processing unit 13 that executes predetermined data processing; ROM (Read Only Memory) 15; tamper-detection circuit 17, switch 19 that switches the power-source supply line to tamper detection circuit 17; power-supply control unit 153 that supplies power to each part; first battery 23, and second battery 25 that is a back-up battery. Information processing unit 13 includes RAM (Random Access Memory) 31, logic IC (Integrated Circuit) 33, and CPU (Central Processing Unit) 35.
ROM 15 stores in advance programs for execution by CPU 35 and the information that is necessary for data processing. RAM 31 is memory for temporarily saving the results of the data processing of CPU 35 and logic IC 33.
Logic IC 33 is a dedicated logic circuit that meets the specifications of the purpose of mobile terminal 100. CPU 35 executes processing in accordance with a program that is read from ROM 15. LCD 11 displays information relating to the data processing realized by information processing unit 13 and the results of data processing to communicate this content to the operator.
The supply of power in the normal state of use when the power-supply switch is ON is next described with reference to FIG. 1.
In the normal state of use in which the power-supply switch of mobile terminal 100 is ON, power from first battery 23 is supplied from power-supply control unit 153 by way of power-source supply line 43 to LCD 11, information processing unit 13, and ROM 15. Switches (not shown) are interposed between power-source supply line 43 and LCD 11 and between power-source supply line 43 and ROM 15 that are ON/OFF controlled by information processing unit 13, and power is supplied to LCD 11 and ROM 15 when the switches are in the ON state. Power-supply control unit 153, by transmitting control signals to switch 19 by way of signal line 41, controls switch 19 to connect tamper-detection unit 17 to either power-source supply line 43 or power-source supply line 45. Here, the battery voltage of first battery 23 is greater than the predetermined voltage, whereby, under the control of power-supply control unit 153, switch 19 connects tamper-detection circuit 17 to power-source supply line 43 that extends from first battery 23. The ON state of the power-supply switch shown in FIG. 1 corresponds to the normal state of use of mobile terminal 100.
Power supply in the suspend state is next described with reference to FIG. 2. With the change to the suspend state, the supply of power continues to information processing unit 13, but the supply of power to LCD 11 and ROM 15 is discontinued by turning OFF a switch (not shown) by information processing unit 13. The power that is supplied to information processing unit 13 is only the power that is requiring to maintain the suspend state and is less than that of the normal state of use. Accordingly, less power is used than in the normal state of use and power consumption can be suppressed.
In FIG. 1 and FIG. 2, the representation of signal lines for transmitting and receiving data or control signals between each of the components has been omitted with the exception of signal line 41 by power-supply control unit 153 a control signal to switch 19, and an aspect of the supply of power from first battery 23 or second battery 25 is shown schematically.
The operations of power-supply control unit 153 are next described for a case in which the battery capacity of first battery 23 is small, i.e., when the battery voltage of first battery 23 is equal to or less than a predetermined voltage.
When the battery voltage of first battery 23 is equal to or less than a predetermined voltage, power-supply control unit 153 halts the supply of power to information processing unit 13. Power-supply control unit 153 further transmits a control signal to switch 19 by way of signal line 41 to implement control over switch 19 such that tamper-detection circuit 17 is connected to power-source supply line 45 that extends from second battery 25. This control is implemented not only when the battery voltage of first battery 23 is equal to or less than a predetermined voltage, but also when first battery 23 is removed from mobile terminal 100. Mobile terminal 100 maintains resistance to tampering even when the battery voltage of first battery 23 is equal to or less than a predetermined voltage or first battery 23 is removed by supplying power to tamper-detection circuit 17 from second battery 25 for back-up.
Japanese Unexamined Patent Application Publication No. 2008-123322 discloses an electronic apparatus in which an auxiliary power-supply unit supplies power to, for example, a tamper-detection unit or a non-volatile memory when the main power-supply unit turns OFF.